1. Field of the Invention
The present invention relates to a network system, and, more specifically, to a network system, a spanning tree configuration method, and a spanning tree configuration node that prevent a network from stopping at the time of reconfiguration of the spanning tree, and further have a load distribution function.
2. Description of the Related Art
Conventionally, this type of spanning tree has been used to prevent data from circulating permanently in a network arranged in the form of a loop (ring).
For example, in a standardization document issued by IEEE, titled “1998 IEEE Std 802.1D”, a control technique referred to as a spanning tree is specified, in which, in order to prevent data from circulating permanently in a network arranged in the form of a loop (ring), a logically tree-like topology is formed by exchanging control information referred to as Bridge Protocol Data Unit (BPDU) between nodes, and logically disabling a portion of the network which is physically loop-like. This is assumed as conventional technology 1.
Moreover, in the standardization document issued by IEEE, titled “2001 IEEE Std 802.1w”, a control technique referred to as a high-speed spanning tree is specified, which accelerates tree creation with the conventional technology 1 by extending a method to exchange the control information, further, rapidly sets up a detour path in the event of a failure by presetting the detour path. This is assumed as conventional technology 2.
Problems such as those described below existed with the conventional technologies mentioned above.
First, there was the problem that, due to congestion, delayed arrival and loss of frames occurred.
With the conventional technology 1, since the spanning tree was stopped and reconstructed from the beginning at the time of addition/remove of nodes and links that belong to the spanning tree, due to the fact that the entire network was stopped for an extended time during reconstruction and congestion occurred, such that sometimes arrival of frames was delayed or frames were lost.
With the conventional technology 2, since the spanning tree was reconstructed gradually while forwarding of a data frame was stopped locally at the time of addition/remove of nodes and links that belong to the spanning tree, a portion of the network was stopped and congested during reconstruction, such that sometimes arrival of frames was delayed or frames were lost.
Second, there was the problem that the network stopped at the time of reconfiguration of the spanning tree, such as addition/remove of nodes that belong to the spanning tree.
With the conventional technology 1, since the spanning tree was stopped and reconstructed from the beginning at the time of addition/remove of nodes that belong to the spanning tree, sometimes the entire network stopped for a long time during reconstruction.
With the conventional technology 2, since the spanning tree was reconstructed gradually while forwarding of data frame was stopped locally at the time of addition/remove of nodes that belong to the spanning tree, sometimes a portion of the network was stopped during reconstruction.
Third, there was the problem that the traffic load could not be distributed.
With the conventional technologies 1 and 2, since the cost was calculated using link capacity and used to select a path at the time of spanning tree construction, it was impossible to change the path for dynamic load distribution according to the traffic.
Fourth, there was the problem that due to reconfiguration of the spanning tree, the network stopped when attempting load distribution.
With the conventional technology 1, when attempting to vary the cost dynamically according to the traffic status, the spanning tree was stopped temporarily and reconstructed to change the path, such that sometimes the entire network stopped for an extended time during reconstruction.
With the conventional technology 2, when attempting to vary the cost dynamically according to the traffic status, a portion of the spanning tree was reconstructed gradually to change the path while forwarding of the data frame was stopped locally, such that sometimes a portion of the network stopped during reconstruction.
Fifth, there was the problem that the path with the minimum cost to a destination was not always selected.
With the conventional technologies 1 and 2, since only one system of spanning tree was set up on the network and only one root node was defined on the network by a priority value and a MAC address, which were preset for each node, to create a single tree, when nodes located at the ends of the tree communicated with each other, sometimes, even if a different, shortest path existed, it was blocked and a lengthy path was taken.
Sixth, there was the problem that the load concentrated in the vicinity of the root node while the link utilization rate was low.
With the conventional technologies 1 and 2, since only one system of spanning tree was set up on the network and only one root node was defined on the network by a priority value and a MAC address, which were preset for each node, to create a single tree, the links not used even though they are located at the ends of the tree appeared, reducing the link utilization rate. On the contrary, sometimes the traffic concentrated in the vicinity of the root node, increasing the possibility of occurrence of congestion.
Seventh, there was the problem that tree construction in the event of a root node failure took time, the network being stopped during that period.
With the conventional technology 1, since only one system of spanning tree was set up on the network and there was only one root node, if a failure occurred at the root node, the spanning tree was stopped and reconstructed from the beginning, such that sometimes the entire network was stopped for an extended time during reconstruction.
With the conventional technology 2, if a failure occurred at the root node, the spanning tree was reconstructed gradually while forwarding of the data frame was stopped locally, such that sometimes a portion of the network was stopped during reconstruction.
Eighth, there was the problem that in the section using IEEE 802.1D, switching of the route was slow in the event of a failure, also taking a long time to reconfigure the spanning tree.
This is because, with the conventional technology 1, it sometimes took several tens of seconds until data could be exchanged at the time of construction of the tree.
Furthermore, ninth, with the conventional technologies 1 and 2, since there was only a single tree, the traffic concentrated and congested in the vicinity of the root node, such that sometimes arrival of frames was delayed or frames were lost.